From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Mon, 27 Aug 2012 13:57:09 +0000 (-0400)
Subject: Document limitation of vppid and ppid context wrt eventual RCU instrumentation
X-Git-Tag: v2.1.0-rc1~3
X-Git-Url: http://git.lttng.org/?p=lttng-modules.git;a=commitdiff_plain;h=1638c9b4fa42c188ffa962552146537f8fb3d26e

Document limitation of vppid and ppid context wrt eventual RCU instrumentation

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/lttng-context-ppid.c b/lttng-context-ppid.c
index 05819048..58ff3fe7 100644
--- a/lttng-context-ppid.c
+++ b/lttng-context-ppid.c
@@ -46,6 +46,15 @@ void ppid_record(struct lttng_ctx_field *field,
 {
 	pid_t ppid;
 
+
+	/*
+	 * TODO: when we eventually add RCU subsystem instrumentation,
+	 * taking the rcu read lock here will trigger RCU tracing
+	 * recursively. We should modify the kernel synchronization so
+	 * it synchronizes both for RCU and RCU sched, and rely on
+	 * rcu_read_lock_sched_notrace.
+	 */
+
 	rcu_read_lock();
 	ppid = task_tgid_nr(current->real_parent);
 	rcu_read_unlock();
diff --git a/lttng-context-vppid.c b/lttng-context-vppid.c
index 365d9739..06377a30 100644
--- a/lttng-context-vppid.c
+++ b/lttng-context-vppid.c
@@ -51,6 +51,15 @@ void vppid_record(struct lttng_ctx_field *field,
 	 * current nsproxy can be NULL when scheduled out of exit. pid_vnr uses
 	 * the current thread nsproxy to perform the lookup.
 	 */
+
+	/*
+	 * TODO: when we eventually add RCU subsystem instrumentation,
+	 * taking the rcu read lock here will trigger RCU tracing
+	 * recursively. We should modify the kernel synchronization so
+	 * it synchronizes both for RCU and RCU sched, and rely on
+	 * rcu_read_lock_sched_notrace.
+	 */
+
 	rcu_read_lock();
 	parent = rcu_dereference(current->real_parent);
 	if (!current->nsproxy)